Phoenix

The Principal had been watching Alex closely for the whole hour he had been doused in those flames, so he noticed a change in Alex immediately.

And what he noticed wasn't good at all.

He magnified his vision by many magnitudes, something any S tier could easily do.

His vision was brought to the cellular level, and he could see each and every one of Alex's cells clearly like he was viewing them through the world's most advanced microscope.

And what he saw left him feeling pity for Alex.

His cells were slowly losing energy, and their regeneration speed was slowing down.

For reference, if it took Alex 1 second to regenerate at the beginning of this whole ordeal, then it now took him 2 seconds.

It didn't seem like much, but it was a big deal.

"What is it, Principal!?" 

Mira looked at the Principal with the small amount of hope she had remaining, some light still flickering in her eyes.